1. Field of the Invention
The invention herein relates to filled polymeric materials. More particularly it relates to such materials filled with specially treated asbestos fiber. It also relates to that specially treated asbestos fiber itself.
Asbestos has long been known as a reinforcing filler or extender for various polymeric resins. Use of fillers is often desirable in order to reduce the amount of resin necessary to manufacture specific products, such as pipe. During periods when resins are in short supply, use of fillers permits more effective use of the available resin. Certain fillers can also improve the flexural and tensile strengths of the resin as well as its creep resistance.
Use of asbestos fiber as a reinforcing filler or extender in thermoplastics has been limited, however, by the fact that asbestos fiber generally has a detrimental effect on the ductility and impact strength of the molded resins. Consequently, asbestos fiber has not been considered satisfactory as a filler for such resinous materials as plastic pipe, where impact resistance is critical.
In addition to the problems of ductility and impact strength reduction, the use of asbestos fibers in thermoplastic resins has also raised additional problems. It has been found quite difficult to disperse untreated fiber adequately in the thermoplastic. Poor fiber dispersion also adversely affects the appearance and reinforcing effect of the fiber in the molded resins.
In addition, uncoated high-surface-area fibers such as asbestos fibers require a considerable amount of energy input to a resin system to properly coat the fibers with the thermoplastic resin matrix. Since many thermoplastic resins (including polyvinyl chloride: "PVC") are shear sensitive, the high energy shearing necessary to properly coat the fibers often results in severe degradation of the resin matrix, unless a large concentration of stabilizer is incorporated into the resin, at a correspondingly higher cost. The shearing effect is illustrated graphically in the single figure of the drawing. Curve A in that drawing shows the amount of energy input over a period of time necessary to incorporate uncoated asbestos fiber into a PVC matrix. Not only is the initial maximum considerably higher than that required for preparation of unfilled PVC, but any extended shearing results in a marked increase in energy input with a corresponding deterioration of the matrix. The unfilled PVC of Curve B, on the other hand, reaches an initial maximum and then drops off to a stable response to continued shearing. (Further reference to this graph will be discussed below.)
2. Description of the Prior Art
Glycols have previously been used as wetting agents in liquid resin for ebonite laminates consisting of rubber polymers and asbestos papers; see the article by W. Ewchuk, The Society of the Plastics Industry, Inc., Reinforced Plastics/Composites Institute, 28th Annual Technical Conference, 1973, (Section 3-D, Pages 1-14). The purpose of the glycol was to promote penetration of the asbestos paper by the liquid polymer. The physical properties of such laminates were found to deteriorate unless the asbestos content was at least 50-70%. The glycols were also shown to improve flexural strength but the effect on impact strength over the non-glycol-containing material was not reported.
U.S. Pat. No. 1,721,675 describes a fibrous brake lining comprising asbestos fibers which is coated or saturated with glycerol, a hygroscopic triol with a low boiling point.
U.S. Pat. No. 3,180,848 describes the use of aliphatic polyhydric alcohols in asbestos reinforced vinyl halides to stabilize the resins against the degrading effect of the iron present in many types of asbestos. Specifically disclosed are those aliphatic polyhydric alcohols having from two to nine hydroxyl groups and including ethylene glycol (diol), diethylene glycol (diol), glycerol (triol), pentaerythritol (tetrol), dipentaerythritol (hexol) and sorbitol (hexol). The polyhydric alcohols are mixed into the resin formulation in amounts up to approximately 10% by weight of the asbestos fiber present. The resin, asbestos fiber and alcohol are all mentioned as separate components of a mixed system, with no suggestion or recognition of coating of the asbestos fiber prior to compounding with the resin.
A number of theoretical aspects of fiber incorporation into resins are discussed in Speri et al., "Effect of Fiber-Matrix Adhesion on the Properties of Short Fiber Reinforced ABS," American Chemical Society Preprint, Division of Organic Coatings and Plastics Chemistry, 166th Meeting, vol. 33, no. 2, pp. 152-163 (August, 1973). The fibers there described were potassium titanate fibers. The other materials present are described only as "proprietary coupling agent," "proprietary ABS lubricant" and "silicone release agent".
Stearic acid lubricants in combination with untreated chrysotile fiber in polyethylene are shown in U.S. Pat. No. 3,654,202.